(1) Field of the Invention
This invention relates generally to the control of plant pests and more particularly to pesticidal seed treatments which provide protection against pest feeding damage to above ground plant parts.
(2) Description of the Related Art
The control of insects and related arthropods is of extreme importance to the agricultural industry. Every year, these pests destroy an estimated 15% of agricultural crops in the United States and even more than that in developing countries. Some of this damage occurs in the soil when plant pathogens, insects and other such soil borne pests attack the seed after planting. Much of the rest of the damage is caused by rootworms; plant pathogens that feed upon or otherwise damage the plant roots; and by cutworms, European corn borers and other pests that feed upon or damage the above ground parts of the plant. General descriptions of the type and mechanisms of attack of pests on agricultural crops are provided by, for example, Metcalf, in Destructive and Useful Insects, (1962); and Agrios, in Plant Pathology, 3rd Ed., Academic Press (1988).
The period during germination of the seed, sprouting and initial growth of the plant is particularly critical because the growing plant is small and even a small amount of damage can cause the loss of the entire plant. Moreover, some natural plant defenses are not fully developed at this stage and the plant is vulnerable to attack. Not surprisingly, the control of pests that attack above ground plant parts during this early stage of plant growth is a well developed area of agriculture.
Currently, the control of pests that attack post emergent crops primarily involves the application of synthetic organic pesticides to the soil, or to the growing plants by foliar spraying. Because of concern about the impact of chemical pesticides on public health and the environment, there has been much effort to reduce the amount of chemical pesticides that are used. A significant portion of this effort has been expended in developing transgenic crops engineered to express insect toxicants from microorganisms. For example, U.S. Pat. No. 5,877,012 to Estruch et al. discloses the cloning and expression of proteins from such organisms as Bacillus, Pseudomonas, Clavibacter and Rhizobium into plants to obtain transgenic plants with resistance to such pests as black cutworms, armyworms, several borers and other insect pests. Publication WO/EP97/07089 by Privalle et al. teaches the transformation of monocotyledons, such as corn, with a recombinant DNA sequence encoding peroxidase for the protection of the plant from feeding by corn borers, earworms and cutworms. Jansens et al., in Crop Sci., 37(5):1616-1624 (1997), reported the production of transgenic corn containing a gene encoding a crystalline protein from Bacillus thuringiensis that controlled both generations of the European corn borer. U.S. Pat. Nos. 5,625,136 and 5,859,336 to Koziel et al. reported that the transformation of corn with a gene from B. thuringiensis that encoded for delta-endotoxins provided the transgenic corn with improved resistance to European corn borer.
A comprehensive report of field trials of transgenic corn that expresses an insecticidal protein from B. thuringiensis has been provided by Armstrong et al., in Crop Science, 35(2):550-557 (1995).
At the present state of plant cellular engineering, however, transgenic crops are typically resistant only to specific pests for that crop, e.g., transgenic corn expressing a Bt toxin against the corn rootworm. It is frequently necessary to apply synthetic pesticides to such transgenic plants to control damage by other pests.
Insecticides such as synthetic pyrethroids, organophosphates and carbamates; fungicides such as azoles and anilopyrimidines; and acaricides such as pyrazoles; and the like, are very effective against certain above ground plant pests when applied at the proper time and with proper procedures. Appropriate pesticides may be applied at the time of planting as surface bands, “T”-bands, or in-furrow, but these applications require the additional operation of applying the pesticide at the same time as the seeds are being sown. This complicates the planting operation and the additional equipment required for pesticide application is costly to purchase and requires maintenance and attention during use. Moreover, care must be taken to incorporate the pesticides properly into the topmost soil layer for optimal activity. (See, for example, the brochure titled Force 3G Insecticide, published by Zeneca Ag Products, Wilmington, Del. (1998)).
The activity of pesticides that have been applied as in-furrow applications at the time of sowing is usually limited to protection of the seed or the roots of the plant. Some protection against above ground pests such as corn borers has been reported, however, for such treatments with insecticides known to be systemic. Keaster and Fairchild, J. Econ. Entomol., 61(2):367-369 (1968). Since such pesticide chemicals are complex molecules that are expensive to produce, purchase and use, it is desirable that their activity is not diluted or lost by migration away from the desired site of action by moisture seepage or by vaporization.
After the plant has emerged from the soil, foliar spraying of pesticides is often used to control those pests that attach the shoots and foliage of the plant. However, a foliar spray must be applied at a certain time that coincides with the presence and activity of the pest in order to have the most beneficial effect. Application at this time may be difficult or impossible if, for example, weather conditions limit access to the field. Moreover, the plants must be monitored closely to observe early signs of pest activity in order to apply the pesticide at a time when the pests are most vulnerable.
Synthetic pyrethroids have been found to give excellent control of Lepidopteran sp. pests such as cutworms when applied as foliar spray or as surface-incorporated granules at the time of planting. However, since this class of insecticides has very high toxicity to fish, for example, great care must be taken to limit the runoff of the insecticide from either granules or spray into surface waters. Moreover, any foliar spraying must be done at times when there is little wind, and then only with proper equipment that is carefully monitored during use.
The control of pests by applying insecticides directly to plant seed has also been described. For example, U.S. Pat. No. 5,696,144 discloses that the European corn borer caused less feeding damage to corn plants grown from seed treated with a 1-arylpyrazole compound at a rate of 500 g per quintal of seed than control plants grown from untreated seed. In addition, U.S. Pat. No. 5,876,739 to Turnblad et al., (and its parent, U.S. Pat. No. 5,849,320) disclose a method for controlling soil-borne insects which involves treating seeds with a coating containing one or more polymeric binders and an insecticide. This reference provides a list of insecticides that it identifies as candidates for use in this coating and also names a number of potential target insects. However, while the U.S. Pat. No. 5,876,739 patent states that treating corn seed with a coating containing a particular insecticide protects corn roots from damage by the corn rootworm, it does not indicate or otherwise suggest that treatment of corn seed with insecticides, and in particular, with water insoluble, non-volatile chemicals, such as most pyrethroids, provided protection to the shoot and/or foliage of the resulting corn plants. Moreover, neither the U.S. Pat. No. 5,696,144 patent nor the U.S. Pat. No. 5,876,739 patent disclosed treating transgenic corn seed or other transgenic plant seeds with insecticides to provide protection against insect feeding damage to the shoots and foliage of the resulting transgenic plant.
Thus, although the art of protecting the shoots and foliage—as well as the seed and roots—of a plant from damage by pests has been advancing rapidly, several problems still remain. For example, it would be useful to provide a method for the control of pest damage to shoots and foliage of plants without the requirement of applying a pesticide at the time of sowing the seed, and in addition to sowing the seed, either as a surface incorporated band, or in-furrow, for example, or requiring a later field application of a pesticide during plant growth. It would also be useful if the method for pest control minimized the danger of pesticide runoff and minimized the migration of the pesticide from the desired zone of activity by moisture seepage or by vaporization. Furthermore, it would be useful if such a method could be coupled with the biopesticidal activity of transgenic plants to selectively broaden the scope of protection that is provided for the shoots and foliage of the resulting transgenic plant.